CHAPTER XXXII 



Motor mechanisms — introduction: the general 

 principles of motor integration 



DEREK DENN Y-B R O \V N I Harvard University Medical Schnol, Boston, Massachusetts 



CHAPTER CONTENTS 



Spinal Integration 



The Spinal Animal 



Spinal Shock 



Deterioration of Spinal Reflexes 



Reflex Pattern 



Postural Reflexes 



Stretch Reflex 



Coordination of Spinal Reflexes 

 Suprasegmental Integration 



Tonic Neck and Labyrinthine Reflexes, and Decerebrate 

 Rigidity 



Righting Reflexes and Midbrain Animal 



Cerebellar Function 



Hypothalamus 



Thalamic (Decorticate) Animal 



Control of Movement by Cortex (Rolandic Area) 



Extrapyramidal Motor Responses 

 Conclusions 



SPINAL INTEGRATION 



The Spinal Animal 



IT IS A COMMONPLACE OBSERVATION in biologv that the 

 caudal animal segments are capable of a certain 

 cles;ree of coordinated behavior following transection 

 of the neuraxis. The writhing hind segment of the 

 snake or worm, the decapitated fly going through the 

 movements of grooming its absent head, the headless 

 chicken flying some yards after the axe has fallen, 

 are within general experience. We can therefore 

 proceed directly froin the assumption that some part 

 of motor behavior is provided by the spinal mecha- 



nism alone to examine its components and organiza- 

 tion. At the outset, however, we are immediately 

 impressed by the lessened range of such spinal 

 behavioral activity in vertebrates as compared with 

 invertebrates, and in monkey and man compared 

 with the vertebrates possessing less complex nervous 

 systems. The phylogenetic change that is iinplied in 

 the term 'progressive encephalization of function' 

 may be more apparent than real, for earlier estiinates 

 of the optimum reflex recovery in spinal man have 

 had to be revised in the last 15 years in the light of 

 improved methods of care of the human patient with 

 transected spinal cord (59, 67). 



The idea of 'sympathies' between different parts 

 of the bod\' had long preceded the processes of 're- 

 flection' put forward by Descartes in 1662 to cate- 

 gorize such inxoluntary efTects as a blink of the eyes 

 in response to a threat. Opinions regarding the por- 

 tion of the nervous system responsible for 'reflection' 

 slowly changed froin the pineal gland to the limb 

 plexuses, later to the central nervous system in a 

 general pattern. Sherrington (88) pointed out that 

 the fundamental experiment was that of Stephen 

 Hales in 1 733 who demonstrated that the responses 

 of the spinal frog are irrevocably lost following de- 

 struction of the spinal cord. In 1750 VV'hytt widened 

 the conception of reflex action and noted the period 

 of suppression of reflexes immediately following de- 

 capitation. Grainger in 1837 showed that the gray 

 matter of the spinal cord was essential to reflex func- 

 tion. As Sherrington reinarked, the importance of 

 the next step, the Bell-Magendie experiment that 

 defined the sensory and motor nerve roots, can 

 hardly be overestimated. 



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